Filter device for a tracheostoma

ABSTRACT

A device for filtering air that is to be breathed through a tracheostoma, to simulate the role of the nose particularly in patients who have received a tracheostomy comprises a filter (20). The filter comprises a pre-filter (21) formed from electrostatically charged fibers, a first layer (22) formed from activated carbon and a second layer (23) a hydrophilic material such as one that is based on regenerated cellulose material. The filter includes a layer of adhesive by which it can be held in place when in use, and a cover layer (24) on its exposed surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a filter device for filtering air that is tobe breathed through a tracheostoma, for example in patients who havereceived a tracheostomy, for example as part of a laryngectomy. Undersuch circumstances, the device can be fitted over a tracheostoma, bodyworn, for example directly over a tracheostoma, or to a tracheostomytube, and serves to simulate some of the functions of the nose. Thedevice can include a valve to assist in diverting the flow of exhaledair, for example to permit speech.

2. Description of Related Art

A tracheostomy is a surgical procedure in which an opening is formedthrough the anterior surface of the neck into the trachea. The openingis referred to as a tracheostoma. A tracheostomy tube can be provided toextend between the tracheostoma and the trachea.

A laryngectomy is a surgical procedure, used for example to treat acarcinoma, which involves removal of the larynx or voice box andcreation of a tracheostoma. A consequence of the procedure is that thetrachea is no longer connected to the pharynx but is diverted to thetracheostoma. After this procedure, normal nasal function is notpossible.

In a subject whose breathing functions normally, the nose and the mucousmembrane lining of the nasal cavity perform important functions inconditioning inhaled air. The convoluted passages and rich blood supplyserve to increase both the temperature and humidity of the inhaled airto minimise the differential in these parameters with those of thesurface of the lungs. Normally some heat and moisture is also capturedfrom exhaled air prior to its release to the atmosphere. The mucouslining of the nasal passages also serves to remove particulate matter,such as fine dust particles, pollutants and micro organisms, from theinhaled airstream, and the action of cilia transports mucous and anyparticles away from the lungs.

The exchange of heat and moisture, and filtration are clearly beneficialto the patient and, in their absence, clinical consequences such asincreased incidence of chest infections, elevated levels of secretionproduction and encrustation are observed.

The upper airways also provide resistance to air flow which promotesgood thoracic muscle tone and allows good respiratory function to bemaintained.

A further consequence of a laryngectomy is that speech is no longeravailable by the normal method of passage of air through the vocal cordsof the larynx. Where clinical conditions permit, it is clearly in thepatient's interest to restore the facility of speech.

It is sometimes possible to insert a voice prosthesis in an artificiallycreated fistula between the upper regions of the trachea and theoesophagus. It then becomes necessary to provide means for directing theflow of exhaled air through the voice prosthesis. This can beconveniently achieved by the incorporation of a valve in an externallyworn device.

When a patient has received a tracheostomy, in effect all inhaled airenters the lungs via the tracheostoma, and the nose is effectively notinvolved in the inhalation process. Exhaled air may pass through thetracheostoma or, if a voice prosthesis has been fitted, the stoma can beoccluded so that the exhaled air is diverted through the voiceprosthesis into the pharynx and the mouth, enabling the patient tospeak. It is desirable that the flow of the exhaled air be controlled bymeans of a tracheostoma valve. In these situations, the valve can bearranged to remain open during breathing but, with a small additionalincrease in exhaled air pressure, can be closed to divert the air flow.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a filter device for filtering airthat is to be breathed through a tracheostoma, which comprises:

(a) a first zone for filtering matter filtered in a normal nasal cavityfrom air passing through the filter; and

(b) a second zone having means for exchange of heat and moisture withthe air.

The first and second zones of the filter may comprise separate first andsecond layers which are juxtaposed one on top of the other andpreferably attached to one another. In another construction, the zonesmay by provided by zones within a single layer. The single layer devicemay be formed by a process which involves carding.

The second zone of the filter is moisturised and warmed by exhaled air.The moisture and warmth collected by the second zone is then imparted toinhaled air, which is filtered by the first zone. Generally, the air isfiltered by the first zone before it is moisturised and warmed by thesecond zone, especially when the filter comprises two layers.

Preferably, the resistance to air flow through the device of theinvention is at least about 0.2 kPa.s.l⁻¹, more preferably at leastabout 0.4 kPa.s.l⁻¹. Preferably, the resistance is not more than about2.0 kPa.s.l⁻¹, more preferably less than about 1.5 kPa.s.l⁻¹, especiallyless than about 1.0 kPa.s.l⁻¹, for example about 0.7 kPa.s.l⁻¹. Theresistance to air flow can be adjusted by selection of materials for thecomponent parts of the filter device, consistent with the partssatisfying other requirements such as filtration and heat and moistureexchange.

Resistance to air flow in breathing can be measured usingrhinomanometry, for example as disclosed in Journal of Laryngology andOrology, August 1987, vol 101, pp 800 to 808. When resistance to airflow breathed through a tracheostoma is to be measured, the method ismodified by inserting the tube of the rhinomanometer into thetracheostoma under the edge of a filter device, where it is sealed usinga grommet. A mask is placed over the tracheostoma and the filter device.The pressure gradient across the filter device is determined bymeasuring the pressures inside and outside the filter device,respectively. The resistance to air flow can then be calculated asdescribed in the paper.

The first zone filters matter from air passing through the filter whichis filtered in a normal nasal cavity. Such matter will generally includefine particles, micro organisms, and pollutants.

Preferably, the first zone of the filter comprises an activated carbonmaterial. Such a material can be produced by heating material such as arayon viscose fabric to carbonise it and to make it porous andabsorbent. Such material can have a filter size of less than about 10⁻⁷m, and an internal surface of area of greater than 1000 m².g⁻¹, forexample about 1200 m².g⁻¹.

An advantage of the use of a carbon material in the filter zone of thedevice is that good filtration of small particles (including for examplebacteria) and absorption of gases can be achieved while not increasingthe resistance to air flow through the device. Indeed, it has been foundthat the resistance to air flow through a device which uses a carbonmaterial in the filter zone can resemble very closely that of the humannose, while maintaining good filter and adsorption performance. Afurther advantage is that, because of the mechanism of adsorption ofcertain materials onto a carbon material, some heat exchange can takeplace.

The carbon can be provided on the surface of or in the interstices of acarrier, which might be for example a foam or fibrous material.

The carbon can be provided as a fabric, for example a woven, non-wovenor knitted fabric. A fabric formed from an activated carbon has astrand-like formation which gives a high external surface area, whichenhances the level of diffusion of gases through the cloth.

The carbon of the first zone can be modified to augment its filtrationcharacteristics, for example by impregnation with silver in order toenhance its properties in relation to bacteria.

The first zone of the filter can be provided by a fabric formed fromfine fibres, such as one formed from microfibres which have a diameterof less than about 25 μm, more preferably less than about 20 μm,especially less than about 12 μm, for example about 4 to 10 μm. Suchfibres can be formed into a non-woven fabric sheet. A suitable fabricfor use in the first zone of the filter is electrostatically charged,especially positively charged.

A component of the filter that is formed from microfibres can includeone or more support layers. For example, a layer formed from microfibrescan be located between two layers of coarsely woven fibres.

The second zone will generally comprise a hydrophilic material, andindeed in many circumstances can consist virtually entirely of one ormore such materials, other than materials intended for example to assistin stabilising the construction of the zone. The second zone cancomprise fibrous material, such as material incorporated into a woven,non-woven or knitted fabric. Suitable materials can include those basedon regenerated cellulose material, especially viscose rayon orpolyester, or a fabric formed from a blend of such fibres, and materialsbased on acrylic acid and its derivatives, for example in powder, gel orfibrous form.

Preferably, the filter size of the first zone is greater than about0.5×10⁻⁶ m, preferably greater than about 10⁻⁶ m. Filter size ismeasured by directing an air stream at a sheet of material. The streamcontains particles with a particle size profile that has beenestablished using a particle counter such as that sold under the trademark ROYCO. The particle size profile resulting from passage of the airstream through the sheet is measured and compared with that of theincident stream, and the effective pore size is the size of the smallestparticles of which 80% are retained by the sheet. It will be understoodthat this test is applicable to materials which have pores (such asmicroporous membranes) and to materials which do not have pores in thestrict sense.

The device of the invention may include a pre-filter having a filtersize that is larger than that of the first zone of the filter. Thepre-filter will generally comprise fibrous material.

When the second zone of the filter is located outside the first zone (sothat air is moisturised and warmed in the second zone before it isfiltered in the first zone), the second zone can provide the pre-filter.More than one zone which includes means for exchange of heat andmoisture with the air can be provided, of which at least one can belocated outside the first zone of the filter to function as apre-filter. When more than one such zone is provided, the materials ofthe zones can be the same or different.

The pre-filter can be formed from fine fibres, especially themicrofibres as referred to above.

A fibrous pre-filter preferably has a weight of greater than about 10g.m⁻², more preferably greater than about 15 g.m⁻². The weight ispreferably less than about 95 g.m⁻², more preferably less than about 65g.m⁻², for example about 45 g.m⁻².

Preferably, the fibres of the pre-filter are electrostatically charged,which has been found to assist filtration.

In another aspect, the invention provides a filter device for filteringair that is to be breathed through a tracheostoma, which comprises:

(a) a pre-filter zone, and

(b) a zone for filtering matter filtered in a normal nasal cavity fromair passing through the filter, the filter size of the filter zone beingsmaller than that of the pre-filter zone.

Preferably, the filter size of the pre-filter is more than about 5×10⁻⁶m, more preferably more than about 10×10⁻⁶ m, especially more than about15×10⁻⁷ m.

Preferably, the ratio of the filter size of the pre-filter to that ofthe first zone of the filter is greater than about 5, more preferablyless than about 10, especially less than about 15.

Suitable materials for the pre-filter include polyolefins, especiallypolypropylenes, and polycarbonates.

Preferably, the device includes at least one cover layer, which can toprotect the filter during assembly and when in use. The cover layermight provide, for example, the protection for a pre-filter formed fromfine fibres.

More than one cover layer can be provided; for example separate coverlayers can be provided, one on each face of the device. The materials ofcover layers provided on respective faces of the device can be differentfrom one another.

When the device includes more than one layer of material, for examplewhen the first and second zones are separate layers, or when the deviceincludes one or both of a pre-filter or a cover layer, adjacent ones ofthe layers may be held in place relative to one another, for example bymeans of adhesive, by welding or by mechanical fastening means. Suitableadhesives include materials which can be activated by the application ofheat, such as fusible materials. Such materials can be incorporated intoor placed on one of the layers, or may be placed between adjacentlayers.

The filter of the invention can be formed as a single layer, whoseproperties change from one zone to another. This might be achieved, forexample, by means of a carding machine. For example, a compositenon-woven fabric can be formed by first laying down fibres of twomaterials in two layers, and then causing the layers to bond to oneanother by means of needles or by fine jets of water at high pressure.

A dual rotor carding method can be used to form a single layer productwith more than one zone, in which two distinct fibre types are presentedto a single dual rotor card, which can be used to form a product inwhich the fibre type changes gradually through the thickness of theproduct, for example from 100% filter--0% hydrophilic fibre on onesurface to 0% filter--100% hydrophilic fibres on the opposite surface.The composite structure can subsequently be consolidated, for example bytreatment with a consolidating substance (which might be an adhesive) orby physical means such as heating.

Preferably, the device includes means for sealing the device around thestoma, allowing the device to be body worn. The seal might be directlyto the skin around the stoma or to a substrate component which ismounted already. The seal will frequently extend around the stomacompletely and continuously, although there will be many situations inwhich it will be satisfactory for the seal to extend only partiallyaround the stoma, provided that the device is not able to movesignificantly during normal physical activities away from the stoma tothe extent that foreign particles can enter the stoma.

A seal can suitably be provided by a quantity of an adhesive materialwhich can be exposed to mount the filter for use. A device that ismounted by means of adhesive can be relatively inconspicuous, and canfor instance be disguised under normal clothing.

The adhesive may be provided to surround the stoma completely, or it maybe provided to form a seal around part only of the stoma, for example asa adhesive strip which extends along one side, or two opposite sides, orthree sides, of the stoma.

Preferably, the adhesive comprises a composition which absorbssignificant quantities of moisture and can therefore reduce skinmaceration, for example a hydrocolloid composition. It can be convenientin some circumstances to include in the device a quantity of ahydrocolloid composition together with another adhesive material withdifferent properties, for example a higher initial tackiness.

The device may include a web of material to which the filter isattached, which is coated with an adhesive for mounting the filter foruse. A suitable web might be an adhesive coated tape.

Preferably, the adhesive material is provided on a surface of acomponent of the device in selected regions of the surface, which canfacilitate moisture vapour transmission, for example when the adhesivethat is used does not absorb significant quantities of moisture.

Alternatively or in addition to the use of an adhesive, the device maybe held in place by components such as a tape, a tie, or strips of aninterengaging hook and loop material (such as that sold under the trademark VELCRO).

The filter device can be arranged to operate with a valve, which mightbe relied on, for example, to divert exhaled air for generation ofspeech. The valve will generally be mounted outside the filter componentof the device. The incorporation of a valve in the device can obviatethe need for manual occlusion in order to divert air flow.

A valve can be attached to the external surface of the device. Forexample, the device might include formations for engaging a valve. Thesemight take the form of, for example, a socket, a bayonet or other twistlock fitting, or a threaded fastener portion. This is particularlyadvantageous when the filter device is secured in place next to a stomaby means of an adhesive around the filter to provide a seal.

Preferably, the filter device includes a housing for a valve. Such ahousing can be can be attached to the outer surface of the device duringassembly, for instance, by welding. The housing can receive atracheostoma valve in it, for example by means of cooperating flanges,and can enable the valve to be attached and detached conveniently andwhile also providing an air tight seal to the filter, and thereby to thestoma itself.

It is also envisaged that a valve might be attached to the filter bymeans of adhesive.

A valve might be provided in a housing which is formed integrally with,or is connected to, means for mounting the device onto a tracheostoma.The housing can include means for receiving a filter component whichincludes a first zone for filtering matter filtered in a normal nasalcavity from air passing through the filter; and (a) a second zone havingmeans for exchange of heat and moisture with the air, or (b) apre-filter zone, or both. For example, the housing might include a slotin which a filter component can be received. A filter component might befitted between the housing and the mounting means with which the housingengages.

The device can be fitted to the exposed end of a tracheostomy tube by anappropriate attachment device. Such a attachment device might comprise:

(a) a first component that can engage the filter device and can befitted around the external circumference of the tube; and

(b) a second component which can engage the first component and theexternal circumference of the tube to provide an air-tight seal.

A suitable attachment device is disclosed in the application filed withthe present application bearing the reference P21558WO which claimspriority from UK patent application no. 9214716.4, and which is entitledTracheostomy tube assembly. Subject matter disclosed in thespecification of that application is incorporated in this specificationby this reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be further described by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of a filter;

FIG. 2 is an exploded view of the layers of the filter of FIG. 1;

FIG. 3 is a cross-section along A--A of FIG. 1;

FIG. 4 is an exploded isometric view of another embodiment of filter;

FIGS. 5 and 6 are views of filter devices which include means forengaging a valve;

FIG. 7 is a side cross sectional view of a filter device in which thefilter component is held in place between a valve housing and a mountingflange; and

FIG. 8 is a graph showing the filtering characteristics of the filtershown in FIGS. 1 to 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring to the drawings, FIGS. 1 to 3 show a filter 2 which comprisesfive layers. The outer cover layer 4 is provided by a non-woven nylonfabric, with an acrylic binder. The inner cover layer 6 is provided by aperforated polyethylene film. The central layer 8 is provided by anon-woven polyester fabric which has been impregnated with carbon.Intermediate layers 10, 12 are provided between the cover layers 4, 6and the central layer 8, provided by a non-woven fabric formed from ablend of viscose rayon and polyester.

The central layer 8 of the filter provides a first zone in whichparticulate matter, pollutants and micro organisms can be filtered fromair passing through the filter. The intermediate layer 10 provides apre-filter whose filter size is larger than that of the first zone ofthe filter. The hydrophilic fibres of the intermediate layer 12 providemeans for exchange of heat and moisture with the air.

The filter provided by the central and intermediate layers are locatedbetween the two cover layers, whose area is bigger than that of thecentral and intermediate layers. The cover layers are attached by meansof a radio frequency weld around their periphery 14 to a backing sheet16 (such as a non-woven backing sheet formed from polyethylene), whichis coated with a hydrocolloid adhesive material 18. A release paper 19is provided to protect the adhesive material before the filter ispositioned for use on the skin of a user over the stoma.

FIG. 4 shows a filter device 20 which comprises a pre-filter 21 formedfrom electrostatically charged microfibres, a first zone 22 formed fromactivated carbon and a second zone 23 formed from viscose fibres. Thefilter further comprises a cover layer 24.

In use, the second zone 23 is positioned adjacent a stoma in a patientwho has had a tracheostomy. The cover stock layer 24 is exposed to theenvironment.

The first zone 22 comprises a layer of activated carbon cloth. Such alayer has a high surface area and is able to filter bacteria, and toabsorb certain pollutant gases such as hydrogen sulphide. The secondzone 23 is comprises fibres of a hydrophilic material such as viscose.

FIG. 5 shows a filter device 50 which includes a socket 52 for receivinga tracheostomy valve 54. The socket is open at its upper end, and canreceive a flange 56 on the valve. The socket is fastened to the filterdevice by welding.

FIG. 6 shows a filter device 60 which includes an upstanding flange 62for engaging a tracheostomy valve. The flange can be threaded to engagethe valve, or it might be continuous and engage a matable flange on thevalve by deformation of one or both of the flanges, for example in themanner of a container used for storage of food.

FIG. 7 shows a filter device which comprises a mounting component 70having a layer of an adhesive material on the surface 72 which isintended to contact the skin of a patient around a tracheostoma. Themounting component has a flange 74 extending from it. The deviceincludes a housing 76 for a valve, the housing including a cooperatingflange 78 to engage the flange 74 on the mounting component. Inalternative arrangement, the mounting component and the housing can beattached to one another by means of an adhesive.

A filter component 80, which might comprise the five layers shown inFIG. 2, or the four layers shown in FIG. 4, is held in place between themounting component 70 and the housing 76 when the two are mated with oneanother.

The housing might include a slot or other formation for receiving thefilter component, so that the filter component can be removed from thefilter device and replaced, without removal of the housing from thestoma. Indeed, especially in this arrangement, the housing and themounting component might be provided by a single component.

EXAMPLE

A filter having the construction shown in and described with referenceto FIGS. 1 to 3 was made using the following materials:

    ______________________________________                                        Central layer 8                                                               Fabric construction                                                                           Non-woven polyester fabric                                                    impregnated with carbon                                       Carbon content  90 to 110 g · m.sup.-2                               Thickness       0.5 to 1.0 mm                                                 Air permeability                                                                              100 to 160 cc · cm.sup.-2 · s.sup.-1                        (Method BS 5636)                                              Surface pore size                                                                             200 × 10.sup.-9 m                                       Surface area    1000 to 1300 m.sup.-2 · g.sup.-1                     CCl.sub.4 absorption                                                                          60% w/w                                                       Strength        9 N · cm.sup.-1 (Method BS 2576)                     Fabric weight   90 to 110 g · m.sup.-2                               Intermediate                                                                  layers 10, 12                                                                 Type            Non-woven fabric                                                              Viscose rayon 95%                                                             Polyester 5%                                                  Fabric weight   45 to 65 g · m.sup.-2                                Fiber staple length                                                                           50 mm                                                         Cover layers 4, 6                                                             OPTION 1                                                                      Type            Point sealed non-woven fabric                                                 Polypropylene core; polyethylene                                              sheath                                                        Fabric weight   50 g · m.sup.-2                                      Sealed area     not more than 14%                                             OPTION 2                                                                      Type            Spun laid non-woven fabric with                                               acrylic binder                                                                100% polyamide                                                Fabric weight   35 g · m.sup.-2                                      ______________________________________                                    

The bicomponent mentioned above as option 1 for the cover layer ispreferred where assembly is by welding and the fabric is required tomaintain its integrity in the region of the welds.

The central layer 8 and the intermediate layers 10, 12 are bonded to oneanother by means of a net like construction of 100% thermo fusiblefibres, by the application of heat and pressure.

The resistance to air flow of the filter was measured using the methoddescribed above. The temperature and humidity of air breathed throughthe filter installed over a tracheostoma using a meter (such as one soldunder the trade mark HM34CX by Viasala), with the probes inserted andsealed through the filter device, into the tracheostoma. The results ofthe tests, compared with those from a patient able to breathe normally,were as follows:

    ______________________________________                                                AIR                                                                           RESISTANCE                                                                              TEMPERATURE                                                         (kPa · s · l.sup.-1)                                                  (°C.)                                                                              HUMIDITY                                        ______________________________________                                        Breathing via                                                                           0.5         35.8        85%                                         nose                                                                          Breathing via                                                                           0.7         34.5        83%                                         tracheostoma                                                                  ______________________________________                                    

FIG. 8 shows the characteristics of the filter shown in FIGS. 1 to 3compared to the nasal function of a human being, plotted in terms of thepercentage of particles of given size that are filtered by the filterand the nose respectively. It will be seen that the filtrationcharacteristics of the device follow very closely those of the humannose. Furthermore, the pressure drop across the filter device is veryclose to that found in normal human breathing.

I claim:
 1. A filter device to filter air that is to be breathed througha tracheostoma, which comprises:(a) a first zone for filtering matterfiltered in a normal nasal cavity from air passing through the filter,(b) a second zone which provides means of exchange of heat and moisturewith the air, said first and second zones providing resistance to airflow through the zones of the device of at least about 0.2 kPa.s.l⁻¹,and (c) sealing means for forming a seal between the device and thestoma substantially continuously around the periphery of the device soas substantially to prevent leakage of air around the sides of thedevice between the device and the stoma, and so that the device providesthe resistance to air flow in breathing when in use on both inhalationand exhalation.
 2. A device as claimed in claim 1, in which the firstzone of the filter comprises an activated carbon material.
 3. A deviceas claimed in claim 2, in which the carbon material is provided as anactivated carbon fabric.
 4. A device as claimed in claim 1, in which thefirst zone of the filter comprises a fabric whose fibres are charged. 5.A device as claimed in claim 4, in which the second zone of the devicecomprises material.
 6. A device as claimed in 5, in which thehydrophilic material comprises regenerated cellulose material.
 7. Adevice as claimed in claim 6, in which the second zone of the filtercomprises fibrous material.
 8. A device as claimed in claim 7, in whichthe filter size of the first zone is greater than about 0.5×10⁻⁶ m.
 9. Adevice as claimed in claim 8, which includes a pre-filter having afilter size that is larger than that of the first zone of the filter.10. A device as claimed in claim 9, which includes at least one coverlayer.
 11. A device as claimed in claim 10, which includes formationsfor mounting a tracheostoma valve.
 12. A device as claimed in claim 11,which includes a housing in which the filter zone of the device,intended for filtering matter filtered in a normal nasal cavity from airpassing through the filter, is received.
 13. A device as claimed inclaim 12, in which the housing includes means for receiving a valve. 14.A device as claimed in claim 13, in which the resistance to air flowthrough the device is less than about 1.0 kPa.s.l⁻¹.
 15. A device asclaimed in claim 14, in which the means for forming a seal comprises aquantity of an adhesive material.
 16. A device as claimed in claim 2,which includes a carrier, particulate carbon being provided on a surfaceof said carrier.
 17. A device as claimed in claim 16, in which thecarrier is porous and has interstices formed therein, the particulatecarbon being provided in said interstices.
 18. A filter device to filterair that is to be breathed through a tracheostoma, said filtercomprising:(a) a first zone for filtering matter filtered from airpassing through said filter; (b) a second zone to exchange heat andmoisture with the air passing through said filter; and (c) a seal tosupport said filter in place over the tracheostoma and to form a sealbetween said filter and the tracheostoma, said seal being providedaround a periphery of the filter so as substantially to prevent leakageof air around sides of the device between the device and thetracheostoma, and to provide resistance to air flow under bothinhalation and exhalation, wherein said first and second zones provide aresistance of more than about 0.2 kPa.s.l⁻¹ to air flowing through saidfirst and second zones.